The present invention relates to a controlling method for an extremely fine flow rate of a liquid and a microvalve device for practicing the flow rate-controlling method without utilizing any mechanical means for closing and opening a microsize flow channel.
Along with the progress in the microtechnology in recent years, it is sometimes required to finely control an extremely small flow rate of a liquid within a microtechnological system. The conventional means for such fine flow rate control is to use a mechanical device which is a mere miniaturization of an ordinary size mechanical valve for opening and closing the flow channel including those utilizing a membrane valve. Since mechanical movements of the component parts are indispensable in these conventional fine flow rate-controlling means or devices, it is sometimes unavoidable that the accuracy of flow rate control is subject to gradual degradation in the long run due to abrasive wearing or corrosion of the parts constituting the valve device eventually leading to a serious trouble of leakage of the liquid as the wearing or corrosion of the parts has proceeded so far.
In addition, the flow rate controlling system in the prior art is intrinsically complicated because an actuator is always employed for operating the movable parts of the valve device for opening and closing the flow channel. Moreover, the accuracy or precision of flow rate control to accomplish a flow rate as desired can be ensured only by the use of a special controlling mechanism for opening and closing the mechanical valve device. Accordingly, the system as a whole unavoidably has a very complicated structure in order to accomplish continuous fine control of the flow rate of a liquid.
On the other hand, a proposal is made in recent years for a microswitching valve chip by utilizing a shape-memory alloy which serves to dynamically switch a multiplicity of flow channels existing within a chemical IC so as to accomplish dynamical conversion of the reaction system. This method, however, cannot be suitable for practical applications unless several problems have been solved in addition to the disadvantages due to the use of a shape-memory alloy which is a very special and expensive material and a valve member of a specific form from a photocurable resin.
The present invention accordingly has an object, in view of the above described problems and disadvantages in the conventional flow rate-controlling methods in a microscopically fine flow channel, to provide a novel flow rate-controlling method in fine flow channels without using any mechanical members or any special materials but by utilizing the property changes of the liquid per se flowing through the flow channels.
Thus, the present invention provides a novel method for finely controlling the flow rate of a liquid, which is subject to solid/liquid phase transition by decreasing or increasing the temperature, which comprises the steps of:
(a) passing the liquid through a microchannel for flowing of the liquid formed in a substrate made of a heat-insulating material; and
(b1) decreasing the temperature of the liquid below the solid/liquid phase transition temperature of the liquid so as to effect closing of the microchannel for liquid flow with the solid formed from the liquid; or
(b2) increasing the temperature of the solidified liquid above the solid/liquid phase transition temperature of the liquid to effect thawing of the solid in the microchannel for liquid flow so as to re-open the microchannel.
The present invention also provides a microvalve device for fine control of the flow rate of a liquid, which is subject to reversible solid/liquid phase transition by decreasing or increasing the temperature of the liquid, which comprises: a substrate plate made of a heat-insulating material and provided with at least one flow channel penetrating the substrate plate and filled with the liquid; and a temperature-controlling means at or in the vicinity of the flow channel capable of decreasing or increasing the temperature of the liquid filling the flow channel below or above the solid/liquid phase transition temperature of the liquid.